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My code:

public enum WAVE_FORMAT : uint { WAVE_INVALIDFORMAT = 0x00000000, /* invalid format */ WAVE_FORMAT_1M08 = 0x00000001, /* 11.025 kHz, Mono, 8-bit */ WAVE_FORMAT_1S08 = 0x00000002 /* 11.025 kHz, Stereo, 8-bit */ } public SayIfSupported(uint myFormat):- foreach(uint format in Enum.GetValues(typeof(WAVE_FORMAT))){ if ((myFormat & format) == format) { Say("Supported: " + ((WAVE_FORMAT)format).ToString()); } }

What is the actual JIT code will do in here : ((WAVE_FORMAT)format).ToString()?

Shall it enumerate again, when trying to cast to appropriate enum value?

How to avoid the extra enumeration elegantly?

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It's not the JITTer that does this. It's the code for Enum.ToString()

You can look at the ReferenceSource to discover the implementation of Enum.ToString().

Ultimately it ends up calling this code if the [Flags] attribute is not applied to the enum. (It's not in your example, but perhaps it should be!)

public virtual string GetEnumName(object value) { if (value == null) throw new ArgumentNullException("value"); if (!IsEnum) throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType"); Contract.EndContractBlock(); Type valueType = value.GetType(); if (!(valueType.IsEnum || Type.IsIntegerType(valueType))) throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnumBaseTypeOrEnum"), "value"); Array values = GetEnumRawConstantValues(); int index = BinarySearch(values, value); if (index >= 0) { string[] names = GetEnumNames(); return names[index]; } return null; }

Note how it does a binary search and uses reflection to get at the enum names. This is not very efficient, but it's better than looping through all the enum values.

If you're worried about the speed, you could use a simple switch, or a dictionary to look up the strings, or just a simple array if the enum values are contiguous.

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2 Comments

Thank you for your answer.. Enum must have unique NAMES and not values. The reference level shows that they look for first item, equal to the requested value, and then return its name, though there could be other names with the same value. So, if I use enumerating by name, which must be unique on Compiler level, then .NET developers just needed to use aka "currentItem" entity to get access to the name and value at the same time. Isn't that would be better?
Otherwise writing code with heap of List.Add("name", value).... terrible, right? but with enum - just Copy any constant codes declared in C++/C, add "enum MyName : type {" and then Paste the bunch of constants from C++ code..